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Issued on 7th September 2011
PRESS RELEASE
TANZANIA RAINFALL OUTLOOK FOR OCTOBER - DECEMBER 2011
This statement gives a brief review of the performance of rainfall season March-May 2011, evolution of the climate systems and outlook for the October to December 2011 rainfall season.
1. REVIEW OF MARCH TO MAY 2011 RAINFALL SEASON
During the March to May 2011 long rain season the Lake Victoria Basin, parts of north-eastern highlands (Same District), parts of Morogoro region and most of southern regions (Ruvuma, Mtwara and Lindi regions) received normal to above normal rains. Parts of Manyara, Dodoma, Singida, Tabora, northern Kigoma and Shinyanga regions experienced extremely below normal rains. However, mainly normal rains were observed over parts of northern coast (Coastal region, isles of Zanzibar and Pemba). However, most areas of western parts of Kilimanjaro and Dar es Salaam regions observed below-normal rainfall. South-western highlands featured mainly normal rains with pockets of above normal rainfall. Recorded rainfall amounts in millimetres with their percentage of long term means are indicated below:
BIMODAL AREAS:
Lake Victoria Basin: Bukoba 1166.1mm (131.3%), Mwanza 364.8mm (95.8%), Musoma 534.9mm (132.0%), Ukiriguru 364.6mm (107.9%) and Shinyanga 189.1mm (37.6%)
Northeastern highlands: Arusha 299.9mm (68.6%), Moshi 501.0mm (82.5%), Lyamungu 502.1mm (50.0%), Kilimanjaro International Air port (KIA) 331.3mm (108.6%), and Same 509.4mm (195.5%).
Northern coast: Zanzibar: 1039.5mm (120.6%), Amani 793.6mm (103.3%), Kizimbani 1199.6mm (135.1%), Dar es Salaam 443.7mm (75.2%), Morogoro 374.8mm (90.7%), Tanga 854.7mm (133.1%) and Pemba 1060.6mm (102.8%).
UNIMODAL AREAS:
Southwestern Highlands: Mbeya 303.0mm (101.9%), Sumbawanga 285.6mm (105.4%), Mahenge 1589.1 mm (154.5%) and Tukuyu 1159.5mm (102.4%).
Western region: Tabora 249.6 mm (78.2%), Kibondo 237.7mm (53.4%) and Kigoma 344.0mm (102.1%).
Southern coast: Kilwa 652.1mm (128.5%), Mtwara 540.6mm (115.1%) and Naliendele 535.5 mm (121.3%).
Central region: Singida 105.7mm (51.3%), Dodoma 148.2mm (83.7%) and Hombolo 233.1mm (122.1%).
Southern region: Songea 389.5mm (106.0%)
It should be noted that: Rainfall amounts below 75% of long term averages are categorized as below normal while those ranging from 75 to 125% are categorized as near normal and those greater than 125% of long term averages are categorized as above normal.
2. OUTLOOK FOR OCTOBER TO DECEMBER 2011 RAINFALL
2.1. Introduction
Climate scientists from National Meteorological Services of the Greater Horn of Africa (GHA), Eastern African countries, Regional and International Meteorological Institutions convened in Entebbe, Uganda from 1st to 3rd September 2011 to formulate aconsensus rainfall season outlook guidance for October – December 2011 over the Eastern African sub - region. A similar meeting for Southern Africa (SADC countries) took place in Windhoek, Namibia from 29th to 30th August 2011. In both fora TMA experts were participated in preaparing and issuing the upcoming October – December rain season.
The above fora were conducted simultaneously with the Tanzania Meteorological Agency Climate experts’ forum.
In all these fora, climate experts reviewed the state of the global climate systems and its implications to the upcoming rainfall season in the sub-regions. Among the principal factors taken into account were the observed and predicted Sea Surface Temperatures (SSTs) in the Global Oceans.
2.2. CLIMATE SYSTEMS
The prevailing neutral ENSO conditions over the tropical Pacific Ocean and projected Sea Surface Temperature (SST) anomalies over Pacific, Indian and Atlantic Oceans as well as other factors that affect the climate in the country including atmospheric circulation processes that bring moisture into the region and local features have been analyzed. In the October-December 2011, season the SSTs where show a trend towards cooling which imply a likelihood of a weak La Nina conditions across the equatorial Pacific Ocean. The current warming over western Indian Ocean (coast of Eastern Africa) coupled with slightly cooling over Indonesia indicates presence of a mild positive Indian Ocean Dipole during the first two months of the season. However, these SSTs over Western Indian Ocean are expected to become neutral towards the end of the year 2011. Expected low level easterly winds towards the country are likely to decline slightly from November 2011. Westerly wind flow is likely to be enhanced and influence rainfall activities over greater part of the country from December 2011. The coming season is likely to be influenced by occurrences of Tropical Cyclones over south western Indian Ocean.
2.3. SEASONAL RAINFALL OUTLOOK
From the prevailing climate systems explained above the seasonal October- December 2011 rains are expected to be as follows:
(i) Short Rains (Vuli)
The October to December season rains (Vuli) is more important for the north-eastern highlands, Northern coastal areas and most parts of Lake Victoria basin. The rains are expected to be above normal over Eastern parts of Lake Victoria Basin, northen coast, isles of Zanzibar and Pemba and western parts of Northeastern Highlands (Arusha region). Normal to above normal rainfall is expected over the most part of the country.
The short rains (Vuli) season is due to commence from second week of September over Lake Victoria, and gradually spread to other areas of bi-modal region.
Lake Victoria Basin: (Kagera, Northern Kigoma, Mara, Mwanza and Northern Shinyanga regions):
Rains are expected to start during the second week of September 2011 over Kagera region and gradually spreading to other areas (Mwanza, Shinyanga, northern Kigoma (Kibondo) and Mara regions) during the second week of October, 2011. The rains are expected to be mainly above- normal over most areas.
Northern coastal areas and hinterland: (Dar es Salaam, Tanga, Coast, northeastern of Morogoro regions and isles of Unguja and Pemba):
The rains are expected to commence during the second week of October 2011. These rains are expected to be above normal over most areas.
Northeastern highlands: (Kilimanjaro, Arusha and Manyara regions): Rains are expected to commence during the third and fourth week of October and are likely to be normal to above normal.
(ii) Seasonal Rains (November – April) Outlook:
The November to April rainfall (Seasonal rains) is more important for the Western, Central, Southwestern highlands, Southern regions and Southern coast. The rains are likely to be normal to above normal over most of unimodal regions. However, parts of southern Lindi, eastern parts of Ruvuma and Mtwara regions rains are expected to be mainly normal during October to December, 2011.
The western areas: (Tabora, Rukwa and Kigoma regions):
Rains are expected to start during the third and fourth week of November and are expected to be normal to above normal.
Central (Singida and Dodoma regions):
Rains are expected to start during the fourth week of November and are likely to be normal to above normal.
Southwestern highlands: (Mbeya, Iringa and Southern Morogoro):
Rains are expected to start during the third week of November and are likely to be normal to above normal.
Southern region and Southern Coast: (Ruvuma, Mtwara and Lindi regions):
Rains are expected to start during the fourth week of November and are likely to be normal to above normal over western parts of Ruvuma region and mainly normal over eastern Ruvuma, southern Lindi and Mtwara regions.
3:ADVISORY
Agriculture and food security
Over much of the country, farmers are advised to continue with normal cropping season as normal to above normal rains are expected. However, above normal rains may lead to excessive soil moisture condition which is likely to impede crop development. Farmers are therefore encouraged to seek advice from agricultural extension officers.
Pastures for Livestock
Pastures for livestock and wildlife are expected to improve over most part of the country, however pastoralists are encouraged to seek advice from livestock extension officers.
Water and Energy
Water for livestock, pasture, wildlife and other economical activities is expected to be adequate over most part of the country. However water should be well managed and rain water harvesting should be practiced where appropriate.
Vuli rains are expected to improve water levels in hydro-power Dams. However such improvement may not be sufficient due to the fact that most Dams are currently below minimum levels.
Local Authorities
Municipalities over areas where above normal rains are expected are advised to open up drainage systems to avoid water accumulation due to surface runoff so as to reduce the impacts of flash floods.
Health sector
There is a high chance of Malaria and cholera, outbreaks over the areas which are expected to receive above normal rainfall while normal transmission elsewhere, necessary precautions should be taken over those areas.
Disaster Management
The Disaster Management Authorities and other stakeholders are advised to take necessary measures that would ensure preparedness, response and mitigation of any negative impacts resulting from the expected weather conditions such as flash flood over areas expected to receive normal to above normal rainfall.
This Outlook is relevant only for seasonal time scales and over relatively large areas. Local and month-to-month variations may occur. It should be noted that heavy and short duration episodic events are common even in below normal rainfall conditions
The Tanzania Meteorological Agency will continue to monitor the evolution of relevant weather systems and issue updates and relevant advisories and additional guidance regularly.
N.B. Farmers and livestock keepers are advised to seek relevant advisories from extension officers.
It should be noted that this year rainfall is likely to be slightly influenced by a mild positive Indian Ocean Dipole associated with cooling over Indonesia and warming over Western Indian Ocean coupled with La Nina conditions. The coming season is expected to be associated with enhanced rainfall over eastern parts of Lake Victoria Basin and parts of Northern coast. While occasional suppression of rainfall over western parts and southern coast of the country areas may occur during October-December 2011.
Dr. Agnes L. Kijazi
DIRECTOR GENERAL
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